IC (Integrated Circuit) dies are typically packaged before installation in order to protect the die from the external environment. The package may be formed of a simple plastic cover, an encapsulating resin, or other materials. Some packages offer more functions such as power or signal conditioning, and provide a transition from the die to a particular type of connection configuration for when the package is installed in a device.
With the continued reduction in size of devices and their associated electronics, packages are required to perform more functions and contain more processing power. Since packages may be much larger than the dies that they contain, some packages contain more than one die. This can be used to combine a central processor with a graphics processor or with a communications die. With enough components, this type of package may be referred to as System in a Package.
Instead of putting multiple dies in a single package, the packages may be stacked. Stacked packages, when properly designed may allow more processing power or electronic components to be placed in less space. PoP (Package-on-Package) is an IC packaging method that vertically combines discrete component packages. This allows the components to use less space or a smaller footprint on a system board.
One common type of PoP uses two packages that each have a bottom BGA (Ball Grid Array) for connection to external components. An interposer is used between the two packages for interconnection between the two vertically discrete components.